I'm so sorry for the tragic loss of your Snoopy.. I can't imagine the devastation of something like that... I normally wouldn't recommend it but I think if you were planning to adopt the girl puppy I would just go ahead with that as planned if you feel able to. It may help you in your grieving process. There is nothing I can say to take away your pain and shock but know of course that you're not a lone. We are all grieving here too and we're here to help to and to listen to whatever feelings and thoughts you have.
I only have one experience of losing a young furbaby- my Arthur, who turned out to be a girl, disappeared one day, she was an indoor/outdoor cat and I felt very, very guilty about letting her out that day because she seemed not as excited to go out as usual. She was a very tough cat. She was indoor/outdoor. Although I adopted her as a tiny kitten, she had a feral mom and for some reason she never became completely tame, I was the only one who could even pick her up and I have a scratch scar on my hand from her from years ago. I loved her a great deal though- we had a special bond. I remember the night I came back from a trip from Europe and picked her up from my friends who had been taking care of her- she had tried to bite my friend's husband when he made her an omlette, lol. and she was SOOO happy to see me and slept by my head all night purring. We later found out that our next door neighbor had put their dog to sleep at this time- they said because he had bitten their son, but we thought he killed my Arthur, and they never told us which is awful. We searched for her for a month, checked shelters etc. but we never found her. I eventually adopted Tess at one of the shelters and she healed me and became the love of my life cat. I used to call Arthur, Arthie.. I miss her still and still feel guilty. She was only about 1 year old at the time she went missing. Just remember that it is normal to feel guilt, it is something we have to process with grief, but Snoopy loved you and he wouldn't want you to feel guilt or to feel bad. I think what happened is pretty unusual and it could have happened even if you were at home with him.
My beloved sweet Tess August 1999 - February 21 2001
My beloved loyal Byron March 1998 - April 28 2008 My sweet beloved girlie Angelina April 2001- September 2012 Me & my sweet beloved Wizberry forever 1998- April 21, 2016 My sweet beloved Snow Goddess Sybil girlie April 2001- May 11,2018